Method for Preparing Single Walled Carbon Nanotubes from a Metal Layer

ABSTRACT

Methods of preparing single walled carbon nanotubes are provided. An arrangement comprising one or more layers of fullerene in contact with one side of a metal layer and a solid carbon source in contact with the other side of metal layer is prepared. The fullerene/metal layer/solid carbon source arrangement is then heated to a temperature below where the fullerenes sublime. Alternatively, a non-solid carbon source may be used in place of a solid carbon source or the metal layer may simply be saturated with carbon atoms. A multiplicity of single walled carbon nanotubes are grown on the fullerene side of the metal layer, wherein at least 80% of the single walled carbon nanotubes in said multiplicity have a diameter within ±5% of a single walled carbon nanotube diameter D present in said multiplicity, said diameter D being in the range between 0.6-2.2 nm.

This application claims the benefit of and priority to U.S. Ser. No.60/743,927, filed Mar. 29, 2006, the contents of which are herebyincorporated by reference. This application is also a continuation inpart of PCT/US2006/012001, filed Mar. 29, 2006, which claims the benefitof and priority to U.S. Ser. No. 60/665,996, filed Mar. 29, 2005, thecontents of both of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of Invention

The invention relates to methods for preparing single walled carbonnanotubes. More specifically, the invention relates to methods forpreparing single walled carbon nanotubes from a metal layer which is incontact with fullerenes on one side and in contact with a solid carbonsource on the other side. Alternatively, instead of a solid carbonsource, the metal layer may be saturated with carbon atoms or may be incontact with a non-solid carbon source.

Carbon Nanotubes

This invention lies in the field of carbon nanotubes (also known asfibrils). Carbon nanotubes are vermicular carbon deposits havingdiameters less than 1.0μ, preferably less than 0.5μ, and even morepreferably less than 0.2μ. Carbon nanotubes can be either multi walled(i.e., have more than one graphite layer on the nanotube axis) or singlewalled (i.e., have only a single graphite layer on the nanotube axis).Other types of carbon nanotubes are also known, such as fishbone fibrils(e.g., resembling nested cones), etc. As produced, carbon nanotubes maybe in the form of discrete nanotubes, aggregates of nanotubes (i.e.,dense, microscopic particulate structure comprising entangled or bundledcarbon nanotubes) or a mixture of both.

Carbon nanotubes are distinguishable from commercially availablecontinuous carbon fibers. For instance, the diameter of continuouscarbon fibers, which is always greater than 1.0μ and typically 5 to 7μ,is far larger than that of carbon nanotubes, which is usually less than1.0μ. Carbon nanotubes also have vastly superior strength andconductivity than carbon fibers.

Carbon nanotubes also differ physically and chemically from other formsof carbon such as standard graphite and carbon black. Standard graphite,because of its structure, can undergo oxidation to almost completesaturation. Moreover, carbon black is an amorphous carbon generally inthe form of spheroidal particles having a graphene structure, such ascarbon layers around a disordered nucleus. On the other hand, carbonnanotubes have one or more layers of ordered graphenic carbon atomsdisposed substantially concentrically about the cylindrical axis of thenanotube. These differences, among others, make graphite and carbonblack poor predictors of carbon nanotube chemistry.

Multi walled and single walled carbon nanotubes differ from each other.For example, multi walled carbon nanotubes have multiple layers ofgraphite along the nanotube axis while single walled carbon nanotubesonly have a single graphitic layer on the nanotube axis.

The methods of producing multi walled carbon nanotubes also differ fromthe methods used to produce single walled carbon nanotubes.Specifically, different combinations of catalysts, catalyst supports,raw materials and reaction conditions are required to yield multi walledversus single walled carbon nanotubes. Certain combinations will alsoyield a mixture of multi walled and single walled carbon nanotubes.

Processes for forming multi walled carbon nanotubes are well known.E.g., Baker and Harris, Chemistry and Physics of Carbon, Walker andThrower ed., Vol. 14, 1978, p. 83; Rodriguez, N., J. Mater. Research,Vol. 8, p. 3233 (1993); Oberlin, A. and Endo, M., J. of Crystal Growth,Vol. 32 (1976), pp. 335-349; U.S. Pat. No. 4,663,230 to Tennent et al.;U.S. Pat. No. 5,171,560 to Tennent et al.; Iijima, Nature 354, 56, 1991;Weaver, Science 265, 1994; de Heer, Walt A., “Nanotubes and the Pursuitof Applications,” MRS Bulletin, April, 2004; etc. All of thesereferences are herein incorporated by reference.

Processes for making single walled carbon nanotubes are also known.E.g., “Single-shell carbon nanotubes of 1-nm diameter”, S Iijima and TIchihashi Nature, vol. 363, p. 603 (1993); “Cobalt-catalysed growth ofcarbon nanotubes with single-atomic-layer walls,” D S Bethune, C HKiang, M S DeVries, G Gorman, R Savoy and R Beyers Nature, vol. 363, p.605 (1993); U.S. Pat. No. 5,424,054 to Bethune et al.; Guo, T.,Nikoleev, P., Thess, A., Colbert, D. T., and Smalley, R. E., Chem. Phys.Lett. 243: 1-12 (1995); Thess, A., Lee, R., Nikolaev, P., Dai, H.,Petit, P., Robert, J., Xu, C., Lee, Y. H., Kim, S. G., Rinzler, A. G.,Colbert, D. T., Scuseria, G. E., Tonarek, D., Fischer, J. E., andSmalley, R. E., Science, 273: 483-487 (1996); Dai., H., Rinzler, A. G.,Nikolaev, P., Thess, A., Colbert, D. T., and Smalley, R. E., Chem. Phys.Lett. 260: 471-475 (1996); U.S. Pat. No. 6,761,870 (also WO 00/26138) toSmalley, et. al; “Controlled production of single-wall carbon nanotubesby catalytic decomposition of CO on bimetallic Co—Mo catalysts,”Chemical Physics Letters, 317 (2000) 497-503; Maruyama, et. al.“Low-temperature synthesis of high-purity single walled carbon nanotubesfrom alcohol,” Chemical Physics Letters, 360, pp. 229-234 (Jul. 10,2002); U.S. Pat. No. 6,333,016 to Resasco, et. al.; R. E. Morjan et al.,Applied Physics A, 78, 253-261 (2004), etc. All of these references arehereby by reference.

Additionally, Maruyama, S., “Morphology and chemical state of Co—Mocatalysts for growth of single-walled carbon nanotubes verticallyaligned on quartz substrates,” Journal of Catalysis, 225, pp. 230-239(2004), described a method of growing single walled nanotube forest on aflat surface under vacuum. A bimetallic catalyst containing Co and Moprecursor was first deposited on a quartz surface followed bycalcination and reduction to form highly dense-packed metal particles.The growth of single-walled carbon nanotubes from these metal particlespresented a density of 1×10¹⁷/m² with length of approximately 5micrometers. K. Hata, “Water-assisted highly efficient synthesis ofimpurity-free single-walled carbon nanotubes,” Science, 306, pp.1362-1364 (2004), described another technique using water-assisted CVDmethod to grow single-walled carbon nanotube forest from a Si wafercoated with iron thin film. They observed water-stimulated enhancedcatalytic activity results in massive growth of superdense(10¹⁴-10¹⁵/m²) and vertically aligned nanotube forests with heights upto 2.5 millimeters. All of these references are hereby by reference.

Other known processes include WO 2006/130150, “Functionalized SingleWalled Carbon Nanotubes” and U.S. Pat. No. 6,221,330, “Process ForProducing Single Wall Nanotubes Using Unsupported Metal Catalysts AndSingle Wall Nanotubes Produced According To This Method” Additionally,in “Synthesis of single-walled carbon nanotubes with narrowdiameter-distribution from fullerene,” Chem. Phys. Lett., 375, pp.553-559 (2003), Maruyama et al. reported using alcohol as carbon sourceto grow single-walled carbon nanotubes at relative low temperatures,e.g. 550-800° C. The diameter distribution of those as-grownsingle-walled nanotubes was found to be very broad (0.8-1.3 nm) anduniformity was poor and temperature dependent. When fullerene wasdirectly applied as carbon source, the authors found some improvement ofdiameter distribution to 0.8-1.1 nm, but the uniformity was stillunclear according to the Raman spectroscopy. All of these references arehereby incorporated by reference.

However, currently known single walled carbon nanotube processes tend toyield a wide distribution of single walled carbon nanotube sizes.Measurements of diameters of single walled carbon nanotubes are usuallydone using Raman spectrometry. A typical Raman spectrometer equippedwith continuous He—Ne laser with wavelength of 632.8 nm is used tocollect Raman excitation. A Raman peak at ˜1580 cm ¹is present in alltypes of graphite samples such as highly oriented pyrolytic graphite(HOPG), pyrolytic graphite and charcoal. This peak is commonly referredto as the ‘G-band’. The peak at 1355 cm⁻¹ occurs when the materialcontains defects in the graphene planes or from the edges of thegraphite crystal. This band is commonly referred to as the ‘D-band’ andthe position of this band has been shown to depend strongly on the laserexcitation wavelength. “Radial breathing modes (RBM)” (typically below300 cm⁻¹) were observed with single-walled nanotubes, where all thecarbon atoms undergo an equal radial displacement. A small change inlaser excitation frequency produces a resonant Raman effect.Investigation in the RBM has shown it to be inversely proportional tothe SWCNT diameter. This relationship is expressed in the followingequation,

ω_(RBM)=(223.75/d) cm⁻¹

where ω_(RBM) is the RBM frequency, and d is the SWCNT diameter (innanometers). The relationship is slightly different for determiningindividual nanotubes. Bandow, et al. “Effect of the growth temperatureon the diameter distribution and chirality of single-wall carbonnanotubes,” Physical Review Letters, 80, pp. 3779-3782 (1998), Jishi, etal. “Phonon modes in carbon nanotubes,” Chemical Physics Letters, 209,pp. 77-82 (1993). All of these references are hereby incorporated byreference.

In the above equation and throughout this specification, diameter of ananotube is defined as the distance between the nuclei of carbon atomsat opposite ends of a tube diameter. It is to be understood that thisdiameter differs from distance of closest approach by a second nanotubewhich is greater because of the repulsion of the respective π clouds asoften defined by TEM.

Table A presents sample diameter and ω_(RBM) correlations as previouslyreported in Tables I and II of Jorio, A, et al., “Structural (n,m)Determination of Isolated Single-Wall Carbon Nanotubes by Resonant RamanScattering,” Physical Review Letters, The American Physical Society,Vol. 86, No. 6, pp. 1118-21 (Feb. 5, 2001), herein incorporated byreference:

TABLE A ω_(RBM) ω_(RBM) d_(t) Θ (calc) (expt.) (n, m) [nm] [deg] [cm⁻¹][cm⁻¹] (18, 6) 1.72 13.9 144.4 144(2) (19, 4) 1.69 9.4 146.8 . . . (20,2) 1.67 4.7 148.3 . . . (21, 0) 1.67 0.0 148.8 148(5) (15, 9) 1.67 21.8148.8 . . .  (12, 12) 1.65 30.0 150.3 151(3) (16, 7) 1.62 17.3 153.0154(5) (17, 5) 1.59 12.5 156.4 156(6)  (13, 10) 1.59 25.7 156.4 156(1)(18, 3) 1.56 7.6 158.8 158(1) (19, 1) 1.55 2.5 160.0 160(3) (14, 8) 1.5321.1 162.0 . . .  (11, 11) 1.51 30.0 164.0 164(1) (15, 6) 1.49 16.1166.7 165(1) (16, 4) 1.46 10.9 170.4 169(1) (17, 2) 1.44 5.5 172.7174(1) (18, 0) 1.43 0.0 173.5 176(1) (14, 1) 1.15 3.4 215.1 210(1) (10,6) 1.11 21.8 223.1 . . .  (9, 7) 1.10 25.9 224.9 . . . (11, 4) 1.07 14.9232.2 229(1) (10, 5) 1.05 19.1 236.1 237(2) (12, 2) 1.04 7.6 238.2 . . . (8, 7) 1.03 27.8 240.3 239(2) (11, 3) 1.01 11.7 244.7 . . .

As the number of complex technical applications for carbon nanotubesincrease, there is a need for an improved method for producing singlewalled carbon nanotubes with a more narrow size or diameter distributionso as to allow for a more precise application of single walled carbonnanotubes.

SUMMARY OF THE INVENTION

The present invention provides novel methods of preparing single walledcarbon nanotubes from an arrangement comprising a metal layer,fullerenes in contact with one side of said metal layer, and a solidcarbon source in contact with the other side of said metal layer. Oncethe fullerene/metal layer/solid carbon source assembly has beenprepared, it is heated to a temperature below where said fullerenessublime. The solid carbon source and fullerenes are permitted todissolve at least in part at the metal layer interface and single walledcarbon nanotubes are grown on the fullerene side of the metal layer. Thetemperature may be increased after the fullerenes have nucleatednanotubes to permit greater growth of single walled carbon nanotubes(e.g., 700-1100° C.).

In an exemplary embodiment, any type of fullerenes may be used (e.g.,C60, C70, C100, C36, etc.). The fullerenes may be deposited in one ormore layers of closely packed arrangements onto the metal layer.

In an exemplary embodiment, the metal layer may be comprised of a metalcatalytic for the growth of single walled carbon nanotubes, such as Fe,Co, Mn, Ni, Cu and Mo. The metal layer is preferably of a thicknesswhich permits the diffusion of carbon from the solid carbon source fromone side of the metal layer to the other side of the metal layer (e.g.,1-20 nm, 2-20 nm, 3-5 nm, etc.).

In an exemplary embodiment, the solid carbon source may be carbon fibersor any other solid carbon source known in the art.

In yet another exemplary embodiment, the single walled carbon nanotubesare prepared from a metal layer in contact with fullerenes and anon-solid carbon source using similar methods as described for a metallayer in contact with a solid carbon source.

In a further exemplary embodiment, the single walled carbon nanotubesare prepared from a metal layer in contact with fullerenes and saturatedwith carbon atoms using similar methods as described for a metal layerin contact with a solid carbon source.

The methods of the present invention grow a multiplicity of singlewalled carbon nanotubes, wherein at least 80% of said single walledcarbon nanotubes in said multiplicity have a diameter within ±5% of asingle walled carbon nanotube diameter D present in the multiplicity.Diameter D may range between 0.6-2.2 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the fullerene/metal layer/solid carbonsource arrangement in accordance with an exemplary embodiment of thepresent invention.

FIG. 2 is an illustration of the dissolving of the fullerenes and thebeginning of single walled carbon nanotube growth in accordance with anexemplary embodiment of the present invention.

FIG. 3 is an illustration of the growth of single walled carbonnanotubes in accordance with an exemplary embodiment of the presentinvention.

FIGS. 4 A and B are SEM micrographs of carbon nanotubes grown onC60/Fe/carbon sandwich-structured catalyst.

FIGS. 5 A and B are transmission electron microscopic images of CNTsgrown from a sandwich catalyst.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a new method for preparing single walledcarbon nanotubes from an arrangement of fullerenes, a metal layer, and asolid carbon source. In this assembly, a metal layer is formed or placedonto the surface of the solid carbon source, resulting in one side ofthe metal layer being in contact with and supported by the solid carbonsource. Fullerenes are placed or deposited onto the other side of themetal layer. As such, the metal layer is said to be in contact withfullerenes on one side and a solid carbon source on the other side. Theassembly of this arrangement can be done in any order.

Once the fullerene/metal layer/solid carbon source arrangement orsandwich has been assembled, it is then heated in an inert atmosphere toa temperature just below (e.g., within 10° C. or within 5° C.) that atwhich the fullerenes sublime. It will be appreciated that this is adynamic system: fullerenes are simultaneously vaporizing and dissolvinginto the metal layer. Thus, the “apparent” sublimation temperature,(e.g., about 650° C. for C60 fullerenes at atmospheric pressure), isbest determined by thermogravimetric analysis of an actual sandwich.

Operable temperature ranges can be between about 500° C. to 700° C., atatmospheric pressure, depending on the fullerenes used. If the growthstep is carried out at elevated pressures, even higher fullerenesublimation temperatures may be encountered. It is believed that changesin pressure may lead to changes in equilibrium partial pressure of thefullerene in the gas phase, and thus affect the driving force forvaporization. In any event, at the aforementioned temperature, thefullerenes and the solid carbon source dissolve into the metal layeruntil the thermodynamic activity of the dissolved carbons exceed that ofcarbons in single walled carbon nanotubes. Specifically, it is believedthat the partially dissolved fullerenes in contact with the metal layerat this stage then nucleate or otherwise promote the growth of singlewalled carbon nanotubes since the thermodynamic activity of carbon inthe walls of the single walled carbon nanotube is lower (e.g., morestable) than in the heated fullerene or solid carbon source.Furthermore, as explained below, the partially dissolved fullerene wouldfittingly serve as an end cap for a single walled carbon nanotube of thesame diameter, and thus is an excellent “seed” for single walled carbonnanotube growth.

It is noted however, that the single walled carbon nanotube may be of adifferent diameter from the original “seeding” fullerene end cap. In thepresent invention, the fullerene can alternatively also serve as anucleation promoter. That is, the fullerenes serve to promote thenucleation and growth of single walled carbon nanotubes. Thus, a bundleof single walled carbon nanotubes having a uniform diameter of 1.6 nmmay result under certain conditions from 0.7 nm fullerenes. Thepromotion effect of fullerenes can be seen from the narrow diameterdistribution of grown single walled carbon nanotubes. This results inthe Raman spectrum of such product usually presenting a single peak inthe RBM region instead of multiple signals indicating several differentdiameter populations.

After growth of single walled carbon nanotubes have been initiated, agaseous carbon source can be introduced. Useful gaseous carbon sourcesare CO, hydrocarbons and alcohols. It will be appreciated thatintroduction of a gaseous carbon source in principle allows the growthprocess to be carried out indefinitely, rather than being limited by thequantity of solid carbon source. A continuous process is thus feasible.

Since the partially dissolved fullerenes provide the starting nucleationpoints for the single walled carbon nanotubes, the growth pattern ofsingle walled carbon nanotubes can be influenced by the arrangement offullerenes on the metal layer. For example, where the fullerenes arearranged in closely packed layers at the surface of the metal layer,single walled carbon nanotubes can grow as a close-packedquasi-crystalline rope or bundle to stabilize the metal-carboninterface. Single walled carbon nanotube growth continues as a result ofcarbon from the solid carbon source dissolving into one side of themetal layer and diffusing to the other side of the metal layer and intothe nucleated tubes.

As explained previously, the initial reaction temperature should bebelow that at which the fullerenes sublime in order to permit thefullerenes to partially dissolve into, for example, a hemisphere orhemispherical configuration which would be a fitting end cap for singlewalled carbon nanotubes and thus serve as a “seed” for the growth (orseed to promote the growth) of single walled carbon nanotubes. However,once single walled carbon nanotubes have begun to grow (e.g., theseeding has been completed), there is no longer a need to remain at thissub-sublimation temperature. The reaction temperature may be increasedin order to result in higher or faster growth rates (e.g., thelengthening or elongation of the nanotube itself). Preferred highertemperatures range between about 700° C. to 1100° C. The single walledcarbon nanotube growth is permitted to continue until a desired orusable length is attained.

Each of the three ingredients are discussed in greater detail below.Other raw materials may also be used.

Fullerenes

Fullerenes are a well known term of art used and recognized in theindustry to refer to a form of carbon typically consisting of onlycarbon atoms bound together to make a roughly spherical ball (e.g., a“buckyball”). As such, the most commonly used fullerenes have sixtycarbon and are known as C60 fullerenes. Any other forms of fullereneswhich contain more or less than sixty carbon atoms, such as C70, C100,C36, etc., may also be used in accordance with the present invention.

Fullerenes have an approximately spherical shape (“spheroidal”).Coincidentally, the end of single walled carbon nanotubes is typicallyin the form of a hemisphere. As such, a half-dissolved fullerene (whichresembles a hemisphere) would be a fitting end cap for a single walledcarbon nanotube of the same diameter. Thus, a partially dissolvedfullerene, by its hemispherical nature, would be an excellent “seed” tofacilitate single walled carbon nanotube growth because itshemispherical shape is consistent with the hemispherical shape of an endof a single walled carbon nanotube. As such, bundles of single walledcarbon nanotubes can be nucleated and grown from a plurality offullerenes.

Additionally, as the seed or starting nucleation source for singlewalled carbon nanotube growth, the size of the fullerenes can be used tocontrol the sizes of the single walled carbon nanotubes. For example, askilled artisan seeking to have predominately larger sized single walledcarbon nanotubes would use C100 fullerenes instead of the smaller C36fullerenes, as the diameter of the C100 fullerenes is larger.

Under this same principle, the use of fullerenes as the seeds ornucleation points also permit greater control over the size/diameterdistribution or variation of the single walled carbon nanotubes. Forexample, using all C60 fullerenes will result in a narrowerdistribution/variation of single walled carbon nanotube sizes/diametersas compared to other processes which do not control the size of thestarting nucleation point or seed.

Metal Layer

The fullerenes are placed on a metal layer which helps to facilitatesingle walled carbon nanotube growth. In the preferred embodiment, thefullerenes are placed onto the metal later without initial contact withany possible contaminant sources. Known methods for accomplishing thistask include sputtering and atomic deposition. Other conventionalmethods may be used. Preferably, the number of fullerene layers on themetal layer is enough to substantially saturate the metal layer.

In the preferred embodiment, the metal layer is comprised of a metalcatalytic for the growth of single walled carbon nanotubes. For example,the metal layer may comprise a metal selected from the group consistingof Fe, Co, Mn, Ni, Cu and Mo. Other metals which can catalyze singlewalled carbon nanotubes may be used as well.

The metal layer may be in the form of a film, coating, sheet, membrane,etc. It is preferred that the metal layer be uniform in composition andsmooth on its surface. The metal layer should be of a thickness thatpermits the diffusion of dissolved carbon from the carbon solid source(discussed below) on one side of the metal layer to the other side ofthe metal layer. The thickness of the metal layer may be between about 1nm to 20 nm, preferably about 2 nm to 10 nm, or more preferably, about 3nm to 5 nm.

Different metals may result in different thickness limitations dependingon its carbon solubility and mass transfer properties. For example, Feis a preferred metal since its carbon solubility is high and permitsmore efficient mass transfer of carbon atoms from one side of the metallayer to the other side.

Solid Carbon Source

In contact with the side of the metal layer opposite the fullerenes is asolid carbon source. The solid carbon source provides the supply ofcarbon atoms which permits the single walled carbon nanotubes to grow.Specifically, the solid carbon source dissolves into the metal layer anddiffuses to the other side of the metal layer to become a part of thesingle walled carbon nanotubes as they grow.

In the preferred embodiment, the solid carbon source is free orsubstantially free of voids which may interrupt or distort thecarbon/metal interface as the carbon dissolves into the metal. The solidcarbon source is also preferably free or substantially free ofnon-carbon heteroatoms which may react with the metal layer todeactivate it or form gases which separate the metal layer from thesolid carbon source. If there are heteroatoms present, it is preferredthat they not participate in the carbon nanotube growth. For example,hydrogen would be a preferred heteroatom because it dissolves into themetal layer, diffuses through it and then leaves the metal/carbonnanotube interface as hydrogen gas. Preferably, the surface of the solidcarbon source in contact with the metal should have a high ratio of edgeto basal plane carbon to stabilize the metal film.

There are a number of solid carbon sources that can be used in thepresent invention. For example, glassy carbon is a viable source if ithas not been graphitized to the extent that its thermodynamic activityis lower than that of the single walled carbon nanotubes. Pure carbonpitches such as those made by pyrolysis of polycyclic aromatichydrocarbons are also a viable solid carbon source, as are cross-linkedcarbon resins made by cyclotrimerizing or oxidatively couplingdiethynylbenzenes. Needle-like crystals of polyparaphenylene made byanodic oxidation of benzene may also be used.

Commercially available carbon fibers are preferred carbon sources. Pitchbased as opposed to PAN based carbon fibers are preferred. The mostuseful carbon fibers are those having as many graphene layer edges aspossible on the fiber surface. This can be determined by SEM. Vaporgrown carbon nanofibers such as Pyrograf I and Pyrograf III from AppliedSciences Corp. Or VGCF from Showa Denka Corp. are also useful carbonsources.

Other Embodiments

Instead of using a solid carbon source, a non-solid carbon source suchas a gaseous or liquid carbon source can be used in place of the solidcarbon to provide the supply of carbon atoms which permit the singlewalled carbon nanotubes to grow. In this embodiment, the non-solidcarbon source need not be limited to contacting the metal layer on theside opposite the fullerenes. All that would be required is that thenon-solid carbon source diffuse into and/or through the metal layer tobecome a part of the single walled carbon nanotubes as they grow.Examples of possible gaseous carbon sources include hydrocarbons, CO andalcohols.

In yet another exemplary embodiment, single walled carbon nanotubes maybe grown from a metal layer that is saturated with carbon atoms. Anyknown methods and physical state of the carbon source (e.g., solid,liquid, gaseous) may be used to saturate the metal layer since all thatis important in this embodiment is that there be a supply of carbonatoms to permit growth of single walled carbon nanotubes.

The Resulting Single Walled Carbon Nanotubes

The methods of the present invention grow a multiplicity of singlewalled carbon nanotubes, wherein at least 80% of said single walledcarbon nanotubes in said multiplicity have a diameter within ±5% of asingle walled carbon nanotube diameter D present in the multiplicity. Inother words, the diameter D represents the diameter of a particularsingle walled carbon nanotube present in the multiplicity by which atleast 80% (preferably 80-90%, more preferably 80-95%, even morepreferably 80-99%) of the remaining single walled carbon nanotubeswithin the multiplicity have diameters within ±5% of D. The diameter Dmay be measured using Raman spectroscopy and is preferably in the rangebetween 0.6-2.2 nm, more preferably 1.0 to 1.8 nm, even more preferably1.2 to 1.6 nm.

EXAMPLES

Specific details of several embodiments of the invention have been setforth in order to provide a thorough understanding of the presentinvention. It will be apparent to one skilled in the art that otherembodiments can be used and changes made without departing from thescope of the present invention. Furthermore, well known features thatcan be provided through the level of skill in the art have been omittedor streamlined for the purpose of simplicity in order to facilitateunderstanding of the present invention.

The following examples further illustrate the various features of theinvention, and are not intended in any way to limit the scope of theinvention which is defined by the appended claims.

Example 1 Preparation of Solid Carbon Source Through Carbonization ofPolymers

Solid carbon source was first prepared via carbonization of polymericcompound. A solution containing 10-30% polymer such as PAM-3k, phenolicresin, polyvinyl chloride and pitch was prepared by dissolvingcorresponding amount of polymer in a suitable solvent such as water,alcohol, ketone, ester, etc. A platinum wire was then immersed into suchsolution and a polymer coating was formed on the surface of metal wireafter solvent evaporation. The thickness of formed polymer coating wasestimated in the range of 1-3 mm. After complete drying, the coated Ptwire was placed mounted inside a metal evaporator, MEM-010 manufacturedby Balzers Union Ltd. By passing current through the Pt wire, the Ptwire was heated through its resistance and the polymer was carbonized.The process was monitored by vacuum pressure until no pressure increasewas recorded.

Example 2 Preparation of a Sandwich-Structured Catalyst Precursor

Inside the metal evaporator, MEM-010, a tungsten wire was mounted on theelectrodes, and some iron or cobalt wire (purity better than 99.99%) waswrapped around the tungsten wire as the metal source for thermalevaporation. The thickness of metal coating was monitored by a quartzpositioner. Metal coating of Fe or Co with thickness of 0.5-5 nm wasproduced on the surface of the carbon-coated Pt wire made in Example 1.Finally, fullerene (purity better than 99.9% from BuckyUSA, Inc) wasplaced in a stainless steel mesh boat that was further tied on atungsten wire for fullerene evaporation. A C₆₀ coating of 5-10 nm wasthen formed on metal/carbon coated platinum wire to form asandwich-structured catalyst precursor as C₆₀/[Fe or Co]/solid carbon onthe platinum wire.

Example 3 Preparation of a Sandwich-Structured Catalyst Precursor UsingCarbon Fibers

The same procedure and setup was applied to make a sandwich-structuredcatalyst in which a pitch carbon fiber, made by Tech TradeInternational, Inc, as the solid carbon was applied to replace thosefrom polymer carbonization as described in Example 2. The catalyst wasprepared as C₆₀/[Fe or Co]/carbon fiber.

Example 4 Making Nanotubes by the Sandwich-Structured CatalystPrecursors

The catalysts made in Example 1, 2 and 3 were heated via resistanceheating and controlled at 500-1000° C. via electric current inside themetal evaporator under vacuum. The treated samples were examined by SEM(FIGS. 4 A and 4 B) and TEM (FIGS. 5 A and 5 B) and multiwalled carbonnanotubes with diameter of 6-10 nm were observed

Example 5 Preparation of a Sandwich-Structured Catalyst Precursor on aFlat Substrate

A sandwich-structured catalyst precursor was prepared similar to thedescription in Example 1-3. A silicon wafer was first deposited withphenolic resin emulsion via dip coating. Then the coated sample washeated in argon at 1000-1200° C. in order to carbonize the polymer intosolid carbon. After the carbon formation, the coated Si wafer was placedin a metal evaporator, e.g. MED-010, and a metal such as Fe, Co, Ni orCu was deposited on the wafer surface via physical vapor deposition. Thethickness of metal coating was monitored by a quartz positioner andcontrolled at 1-5 nm. Without taking the wafer outside the vacuumchamber, another C₆₀ coating was placed on top of metal coatingsubsequently as described in earlier examples. The thickness of C₆₀ wasapproximately 5-10 nm. The final catalyst format was C₆₀/[Fe, Co, Ni orCu]/solid carbon/Si.

Example 6 Making Carbon Nanotubes from Si Wafer SupportedSandwich-Structured Catalyst Precursor

The Si wafer supported catalyst is placed in a 1-inch quartz reactorthat has been purged by argon for 10 minutes. Then the reactor is sealedat both ends and the temperature is raised quickly to 800° C. and thesample is allowed to react for 10 minutes under argon. After cooled toroom temperature, the sample is examined using Raman, and exhibitscharacteristic features of single-wall carbon nanotubes with diameter of1.4±0.2 nm.

1-45. (canceled)
 46. A composition of matter comprising: a multiplicityof single wall carbon nanotubes, wherein at least 80% of the singlewalled carbon nanotubes in said multiplicity have a diameter within ±5%of a single walled carbon nanotube diameter D present in saidmultiplicity, said diameter D being in the range between 0.6-2.2 nm. 47.The composition of matter of claim 20, wherein the diameter D is withinthe range of 1.0 to 1.8 nm.
 48. The composition of matter of claim 20,wherein the diameter D is within the range of 1.2 to 1.6 nm.